Given the established underutilization of evidence-based practices (EBPs) for youth mental health disorders, the effective dissemination and implementation of EBPs has become a focal point for researchers, policymakers, and administrators. Los Angeles County (LAC) is on the leading edge of policy-influenced mental health service delivery reform. While a surge in EBP training and implementation support offers community providers new opportunities to incorporate EBP into their clinical work, these providers also find themselves left to navigate an increasingly complex and demanding practice environment. During this period of significant change in the nation’s largest county mental health system, it is critical to understand the experiences of the providers tasked with delivering innovative services to those in need. This dissertation sought to explore providers’ implementation experiences through a series of three studies. The first study examined differences among provider attitudes toward six specific EBPs being implemented in LAC, demonstrating that providers could reliably differentiate the appeal and limitations of the various EBPs over and above their attitudes toward EBP in general. Additionally, appealing features of an EBP were associated with self-reported use of that EBP. Study two used an inductive coding approach to explore providers’ open-ended feedback on their training and implementation experiences in LAC, revealing a predominance of negative comments overall. However, the valence of feedback varied considerably across response categories, with unanimous negativity regarding the local treatment context as compared with more balanced comments about the fit and therapeutic consequences of available EBPs. Study three employed a focus group approach to solicit provider experiences implementing an innovative modular EBP during a randomized clinical effectiveness trial in Los Angeles. Qualitative feedback indicated that the treatment’s fit to diverse client populations and ongoing consultation support were of central importance during the implementation process. Design-focused and supportive strategies to address provider concerns were proposed. Taken together, the studies comprising this dissertation suggest that stakeholders may improve the implementation process through enhancing EBP design in accordance with provider feedback (e.g., improving client fit), addressing contextual demands that interfere with providers’ ability to implement EBP, and continuing to invite provider feedback throughout the implementation process.